Electrophotographic techniques and electrostatic recording techniques use developers that make electrostatic images or electrostatic latent images visible. Developers can be categorized as either two-component developers or one-component developers. Two-component developers include toner and carrier particles. One-component developers include only toner. One-component developers can be sub-categorized into magnetic developers that contain a magnetic component and non-magnetic developers that do not contain a magnetic component. Non-magnetic one-component developers generally include a fluidizer to increase fluidity of toner, which may be colloidal silica.
In general, “toner” refers to color particles that are prepared by dispersing a pigment and additives in latex and by forming the dispersion product into particles. The pigment can be carbon black. Toner can be prepared using a grinding method or a polymerizing method. In the grinding method, a synthesized resin, a pigment, and if necessary, additives, are dissolved and mixed. The mixture is ground and the resultant particles are classified as having a desired diameter. In the polymerizing method, a polymerizable monomer, a pigment a polymerization initiator, and if necessary, additives, such as a crosslinking agent or an antistatic agent, are homogeneously dissolved or dispersed to form a polymerizable monomer composition. The polymerizable monomer composition is dispersed with an agitator in an aqueous dispersion medium containing a dispersion stabilizer so as to form droplet particles of the polymerizable monomer composition. The temperature is then increased and a suspension-polymerization process is performed thereon to obtain color polymerization particles having desired particle diameters or polymerization toner.
Image forming apparatuses such as an electrophotographic apparatus or an electrostatic recording apparatus, form an image using the following method. First, a homogeneously charged photoreceptor is exposed to light and a latent image is thus formed Then, toner is attached to the latent image to form a toner image. The toner image is transferred to a transfer medium such as a transfer sheet. Then, the “un-fixed” toner image is fixed onto the transfer medium by, for example, heating, pressing, or solvent evaporating. In the fixing process in general, the transfer medium, to which the toner image is transferred, passes between a fixing roll and a pressing roll. Toner on the toner image is heated and pressed, which fuses the toner image onto the transfer medium.
Some image forming apparatuses, such as electrical photocopiers, need to have accurate and precise image forming characteristics. Conventionally, toner used in an image forming apparatus has been prepared using the grinding method. However, toner particles obtained from the grinding method have a wide particle-diameter distribution. Therefore, to obtain appropriate development characteristics, toner particles should be classified to reduce the particle-diameter distribution. However, when toner particles for an electrophotographic technique or an electrostatic technique are prepared using conventional mixing and grinding processes, it is difficult to accurately control particle diameters and the distribution of particle diameters. The yield of small particles is low due to the need for the classification process. In addition, there are limitations on modifying or adjusting the toner design for improving charging and fixing characteristics.
For toner prepared by the polymerization process, particle diameters can be easily controlled, and complex processes, such as a classifying, are not used. As described above, when toner is prepared using a polymerizing process, toner having desirable particle diameters and desirable particle-diameter distribution can be obtained without grinding or the classifying process. However, polymerization toner should still have fixing characteristics and durability to obtain desired printing performance and high image quality. To this end, there is a need for toner having optimized rheological characteristics.